ORIGINAL: Ausie-guy
Those charts are only a ball park figure and IMHO they are totally missleading.
I had a gentleman pm me yesterday about his set up 70lb, 27.5" draw and 27" arrow (5575), when I ran his numbers the spine was weak.
I suggest that if the chart say's you need a 5575 (400 spine) arrow go to the next stiffest.
This is one of the reason most people have trouble tuning their bows.
Couldn't agree more Aussie. Especially if you are shooting a drop-away. What I have found a drop-away rest prefers a stiff spined arrow.